I am building a simple IR transmitter and receiver to be able to detect things. The idea is that : I put a receiver on an object I lose often (say keys,remotes etc.) and when I want to find I use the transmitter to locate it. I could put some beep sounds when the receiver detects the IR signal.

Now a goole search is just too vague and broad. What I have gathered is that I could use a simple phototransistor but they might not be that useful in sunlight. If I go about a proper IR receiver module (e.g. TSOP11..) then they demand a suitable data format.

So,
Question 1 ) shud I use the phototransistor ? I can make the scope (or range) narrower by putting tube around it.
Question 2 ) If I use tsop1138 how can i make the transmitter emit pulses (in other words how do I make use of ..555timer to make pulses ) ?

The real limitation with IR is that the receiver must face the transmitter. Any lost object will be at some random orientation or be covered by some other object.

RF is possibly a better solution, as an antenna works even if covered. I'm not pushing the device at the link, but you might want to think about changing from IR for your project - http://www.keyringer.com/

Ya , the IR requires a LOS ( line of Site ) which call for the primary objective of the Project ( finding the missing item) . IR are used when the target is finite and fixed at the given distance. So as suggested you can go for RF which is the best solution .

My daughter bought a cheap keys finder. It is supposed to beep and light its LED when you whistle. I whistled until I was faint but it didn't work. But it was triggered continuously by my daughter's voice and the TV's sound.